1. Field of the Invention
This invention relates to an assay system, and more specifically, to determining the integrated glycemic condition of a diabetic by measuring glucose and protein-bound glucose concentration levels.
2. Background Information
Individuals suffering from diabetes mellitus have an abnormally high blood sugar level generally because the pancreas does not secrete sufficient amounts of the active hormone insulin into the bloodstream to regulate carbohydrate metabolism. If an abnormally high blood sugar level, known as a hyperglycemic condition, is allowed to continue for prolonged periods, the individual will suffer from the chronic complications of diabetes, including retinopathy, nephropathy, neuropathy and cardiovascular disease. Studies indicate that diabetic patients who are able to maintain near normal glycemic control greatly reduce the likelihood of these dire complications. Therefore, several tests have been developed to measure and control glycemic condition.
One common medical test to control glycemic condition is the direct measurement of blood glucose levels by diabetics. Because blood glucose levels fluctuate significantly throughout a given day, being influenced by diet, activity, and treatment, depending on the nature and severity of the individual case, some patients measure their blood glucose levels up to seven times a day. Based on the observed pattern in the measured glucose levels, the patient and physician together make adjustments in diet, exercise and insulin intake to better manage the disease. Clearly, this information should be available to the patient immediately.
However, because of the frequent fluctuation of glucose levels in a given day, tests which are independent of a patient's diet, activity, and/or treatment and which provide longer term indications of blood glucose levels have also been developed. These tests measure the concentration of glycated proteins or "protein-bound glucose" (PBG). Proteins, such as those present in whole blood, serum and other biological fluids react with glucose, under non-enzymatic conditions, to produce glycated proteins. The extent of the reaction is directly dependent upon the glucose concentration of the blood.
One of the first glycated protein tests developed measures glycated hemoglobin, namely Hemoglobin A.sub.1c (HbA.sub.1c), which reflects glycemic control over approximately a 2 to 3 month period. Other such tests measure serum proteins, such as total glycated serum protein, or a specific glycated serum protein, namely glycated albumin. Glycated albumin reflects an intermediate glycemic control over approximately a 2 to 3 week period.
Yet another way to indirectly assess blood sugar concentration is to analyze fructosamine concentration. Glycated proteins are also known as fructosamines or ketoamines. The blood proteins are glycated in vivo by a non-enzymatic reaction between glucose and available amino groups of blood proteins, principally the .epsilon.-amino groups of lysine residues and the .alpha.-amino groups of the protein's terminal amino acid. The glucose binds to an amino group of the protein to form a Schiff base, i.e., a glucosylamine or aldimine, that undergoes molecular rearrangement to form a stable ketoamine. This reaction sequence is illustrated in FIG. 1a. In the art, such ketoamines are generically known as "fructosamines." The degree of protein glycation and fructosamine formation is directly proportional to blood glucose concentration. Measurement of serum or plasma fructosamine levels is useful for monitoring diabetic control because fructosamine concentrations in serum or plasma reflect an average of blood glucose level over approximately a half month period.
While these individual tests to directly and indirectly measure glucose have been developed, there is no convenient test system available which allows a diabetic patient or a physician to assess both the immediate glucose level as well as an intermediate or long-term glycemic condition. Currently, the glucose test is routinely run by the doctor or the patient, however, the glycated protein testing is typically performed in a clinical lab using complicated techniques and expensive instrumentation. Results from these clinical lab tests are usually not available to the doctor and patient for several days. This delay in information transfer decreases the value of the test result. The physician can even neglect to relay the test result to the patient until the next visit, which could be several months. Scandinavian investigators recently showed that doctors and patients who were made aware of their glycated protein test results had better glycemic control than those who were unaware of such results. It is also now believed that glycated proteins can be the causative agents in disease complications. Therefore, a need exists for conveniently and quickly measuring glycated protein alone, or in combination with glucose for determining the integrated glycemic condition of a subject.
Currently, no test system exists which determines the integrated glycemic condition of a subject, providing the subject with a complete picture of his or her glycemic status, thus allowing for the best possible monitoring and treatment. Particularly useful would be a single instrument for determining a subject's integrated glycemic condition which could be used at the doctor's office, or better yet, at home by the diabetic patient. The present invention satisfies these needs and provides related advantages as well.